1. Field of the Invention
The present invention relates to a boom assembly employed in a loading/unloading vehicle for an agricultural, civil engineering work, etc., such as a tractor-mounted loader comprised of a tractor equipped with a front loader and/or a backhoe, a self-propelled loader (wheeled loader, a self-propelled backhoe, a power shovel, etc.).
2. Description of the Related Art
Conventionally, as a boom assembly used in a tractor-mounted loader, there is known a boom assembly which is bent at a longitudinal center portion thereof to present an upwardly convex arc shape and which includes a front boom body provided on the front side from the longitudinal center portion and a rear boom body provided on the rear side from the longitudinal center portion (see e.g. Japanese Patent Application “Kokai” No. 11-158907, in particular its FIGS. 9 and 11).
The front and rear boom bodies of this boom assembly are formed by bending a plate member into a cylindrical shape, or by placing a pair of right and left members, each formed by bending a plate member into an angular hooked cross sectional shape, into abutment with each other and then fixing these together by welding.
Further, with this conventional boom assembly, each of the front and rear boom bodies has upper and lower faces which are formed straight, and as these front and rear boom bodies are connected to each other via a connecting member at the longitudinal center portion of the boom assembly, there is formed the boom assembly which is bent at the longitudinal center portion into the upwardly convex arc shape.
As another boom assembly to be used in a tractor-mounted loader, there is known a boom assembly taking an advantage of a curved appearance (see Japanese Utility Model Application “Kokai” No. 6-53648, in particular its FIG. 3).
This boom assembly includes right and left lateral plates, a top plate and a bottom plate which plates are comprised of separate members. The right and left lateral plates are formed in a curved appearance and the top plate and the bottom plate are bent in correspondence with the shapes of the edges of the right and left lateral plates. Then, these top and bottom plates are disposed between the right and left lateral plates, and right and left lateral edges of the top and bottom plate are fixedly welded to the inner faces of the lateral plates.
For a tractor-mounted loader for use in a tractor having a curved appearance in e.g. the top face of the hood, there is a desire to provide the boom assembly with a curved shape suitable for aesthetic matching with the curved shape of the hood.
In the case of the boom assembly disclosed in Japanese Utility Model Application “Kokai” No. 6-53648 described above, it is possible to provide such aesthetic matching between this boom assembly and the curved shape of the hood. However, weld beads are present on the top surface of the boom assembly. These beads not only deteriorate the aesthetic impression of the assembly, but also invite high manufacture cost due to the large amount of welding needed.
In order to solve the above problem, it may be conceivable to modify the boom assembly disclosed in the first cited document, i.e. Japanese Patent Application “Kokai” No. 11-158907 by bending the front and rear boom bodies thereof so as to provide the boom assembly with a shape aesthetically matched with the curved shape of the hood. However, such bending of the cylindrical boom bodies will be difficult.